Electrolytic capacitors are often formed from valve action materials that are capable of being oxidized to form a dielectric layer. Typical valve action metals are niobium and tantalum. More recently, capacitors have been developed that employ an anode made from an electrically conductive oxide of niobium and a niobium pentoxide dielectric. Niobium oxide has a unique structure as the coordination of both Nb and O atoms appears to be square planar. The arrangement of atoms is that of a defect rock salt structure in which all the atoms at the center and vertices of the unit cells are removed. It has been shown that the formation of the ordered defect structure augments Nb—Nb bonding and stabilizes the square planar oxygen atom by Nb—O π-bonding. Thus, the compound is actually an aggregate of Nb6O12 clusters. By the anodic oxidation in appropriate voltage, NbO is oxidized to Nb2O5nH2O. Upon heating, the hydrated niobium pentoxide slowly loses water; then, the Nb2O5 goes through a series of structural changes and loses a certain amount of oxygen with the formation of oxygen-deficient nonstoichiometric niobium oxide. Unfortunately, this can lead to leakage current instability at accelerated temperature and voltage load.
As such, a need currently exists for an electrolytic capacitor having low leakage current with a corresponding high volumetric efficiency.